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United States Patent |
6,257,521
|
Breckenridge, Jr.
|
July 10, 2001
|
Shimmy-free aircraft tail wheel assembly
Abstract
A vibration-preventing tail wheel assembly prevents an aircraft tail wheel
from shimmying during the takeoffs and landings. The unit retrofits and
mounts between the aircraft tail spring and the original equipment tail
wheel fork. A rigid hub assembly comprising a sleeve-like, central hub is
rotatably coupled to the spindle assembly. The spindle assembly has a
mounting flange connected to the aircraft tail wheel fork. A rigid arm
projecting from the hub is bolted to the tail spring. The spindle assembly
comprises a rigid sleeve coaxially extending from a mounting flange
through and within the hub assembly. A pair of bearing assemblies fitted
within suitable recesses on opposite ends of the central hub contact a
special bushing. An internal, elongated bolt extending upwardly from the
spindle assembly terminates in a threaded terminus engaged by a
castellated nut that axially secures pressures the bushing and preloads
the bearings, that are secured within suitable races fitted on opposite
ends of the central hub. The specially designed bushing goes under the
castellated nut and fits into the upper bearing to give the alignment and
proper strength needed to complete the assembly. A "pre-load" condition is
then introduced to the bearings by applying a minimum of 100 fps torque to
the castellated nut, compressing the bearings together axially but
allowing rotation about the bolt in response to predetermined forces.
Inventors:
|
Breckenridge, Jr.; Gerald H. (135 South St., Beedeville, AR 72014)
|
Appl. No.:
|
520041 |
Filed:
|
March 7, 2000 |
Current U.S. Class: |
244/109 |
Intern'l Class: |
B64C 025/00 |
Field of Search: |
244/109,100 R,104 R
|
References Cited
U.S. Patent Documents
2105374 | Jan., 1938 | Saulnier | 244/109.
|
2329823 | Sep., 1943 | Camburn | 244/109.
|
2394825 | Feb., 1946 | Trader | 244/109.
|
2473645 | Jun., 1949 | Hollerith | 244/109.
|
2494482 | Jan., 1950 | Maule | 244/109.
|
2498112 | Feb., 1950 | Maule | 244/109.
|
2502523 | Apr., 1950 | Irwin | 244/109.
|
2543233 | Feb., 1951 | Dowty | 244/109.
|
2745612 | May., 1956 | Cupp | 244/109.
|
Primary Examiner: Jordan; Charles T.
Assistant Examiner: Best; Christian M.
Attorney, Agent or Firm: Carver; Stephen D.
Claims
What is claimed is:
1. A shimmy-free aircraft tail wheel mounting assembly comprising:
a rigid, lower spindle assembly comprising a rigid, elongated, upwardly
projecting sleeve and a lower mounting flange adapted to be secured to a
conventional aircraft tail wheel fork to secure the tail wheel;
an upper hub assembly coupled to said spindle assembly, the hub assembly
comprising a rigid, central barrel-like hub, and rigid arm projecting
angularly away from said hub for connection to the aircraft tail;
said spindle sleeve extending coaxially within said hub;
bearing means for axially securing said spindle assembly relative to said
hub, while allowing relative rotation between said spindle assembly and
said hub assembly;
whereby the tail wheel fork is enabled to rotate to compensate for stress
forces experienced by said tail wheel, while the tail wheel is secured
against vibration in flight.
2. The tail wheel mounting assembly as defined in claim 1 wherein the hub
arm is channel like in cross section, comprising a pair of spaced apart,
parallel side walls integral with a central planar portion.
3. The tail wheel mounting assembly as defined in claim 1 wherein the hub
comprises an internal bore, an internal ring, and a pair of spaced apart
recesses on opposite ends of said ring within said bore.
4. The tail wheel assembly as defmed in claim 3 wherein said bearing means
comprises a bearing and a bearing race fitted within each of said hub
races and nested against a shoulder provided by said internal ring.
5. The tail wheel assembly as defined in claim 4 wherein said spindle
sleeve is secured by a coaxial, longitudinally-extending bolt centered
within and penetrating said bearing means and axially securing said
spindle assembly relative to said hub assembly.
6. The tail wheel assembly as defined in claim 5 further comprising a
dividing flange between said spindle assembly and said hub assembly.
7. The tail wheel assembly as defined in claim 6 wherein said spindle
assembly sleeve comprises a plurality of rigid, elongated reinforcing
webs.
8. A shimmy-free aircraft tail wheel mounting assembly comprising:
a lower spindle assembly comprising a rigid, elongated, upwardly projecting
sleeve and means for securing the sleeve to a conventional aircraft tail
wheel fork;
an upper hub assembly rotatably coupled to said spindle assembly, the hub
assembly comprising a rigid, central barrel-like hub, and means projecting
away from said hub for connecting the hub to an aircraft tail spring;
said spindle sleeve extending coaxially within said hub;
upper and lower bearings within said hub for axially securing said spindle
assembly relative to said hub, while allowing relative rotation between
said spindle assembly and said hub assembly;
an elongated, rigid bolt centered within said hub and penetrating said
bearings for axially securing said spindle assembly relative to said hub
assembly; and,
nut means threadably engaging said bolt for preloading said mounting
assembly by compressing said bearings;
whereby the spindle is enabled to rotate about the bolt in response to
predetermined forces.
9. The tail wheel mounting assembly as defined in claim 8 wherein the hub
comprises an internal bore coaxially penetrated by the bolt, an internal
ring, and a pair of spaced apart recesses on opposite ends of said ring
within said bore that seat the bearings.
10. The tail wheel mounting assembly as defined in claim 8 further
comprising a two part bushing for compressing the bearings.
11. The tail wheel mounting assembly as defined in claim 10 wherein the
bushing comprises an upper washer portion and a lower, concentric reduced
diameter portion that engages the upper bearing and radially centers the
bearings.
12. The tail wheel assembly as defined in claim 11 further comprising a
dividing flange between said spindle assembly and said hub assembly.
13. The tail wheel assembly as defined in claim 12 wherein said spindle
assembly sleeve comprises a plurality of rigid, elongated reinforcing
webs.
14. A shimmy-free aircraft tail wheel mounting assembly comprising:
a spindle assembly comprising a rigid, elongated, upwardly projecting
sleeve and means for securing the sleeve to a conventional aircraft tail
wheel fork;
a hub assembly adapted to be rotatably coupled to said spindle assembly,
the hub assembly comprising an internal bore, an internal ring, and a pair
of spaced apart recesses on opposite ends of said ring within said bore;
means for connecting the hub assembly to an aircraft tail spring;
said spindle sleeve extending coaxially within said bore;
upper and lower bearings are seated within said recesses for securing said
spindle assembly and enabling relative rotation between said spindle
assembly and said hub assembly;
an elongated, rigid bolt centered within said hub assembly and penetrating
said bearings for axially securing said spindle assembly relative to said
hub assembly;
nut means threadably engaging said bolt for preloading said mounting
assembly by compressing said bearings;
bushing means pressured by said nut means for axially compressing said
bearings while centering the bearings when the nut means is tightened for
preloading;
whereby the spindle is enabled to rotate about the bolt in response to
predetermined forces.
15. The tail wheel mounting assembly as defined in claim 14 wherein the
bushing comprises an upper washer portion and a lower, concentric reduced
diameter portion that engages the upper bearing and radially centers the
bearings.
16. The tail wheel assembly as defined in claim 15 further comprising a
dividing flange between said spindle assembly and said hub assembly.
17. The tail wheel assembly as defined in claim 16 wherein said spindle
assembly sleeve comprises a plurality of rigid, elongated reinforcing
webs.
Description
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to landing gear construction for
small aircraft. More particularly, my invention relates to a tail wheel
assembly for small aircraft that secures the tail wheel and eliminates
jarring or jerking, and other unwanted vibration, thereby preventing tail
wheel shimmying.
II. Description of the Prior Art
In general, the concept of stability relates to the characteristics of an
aircraft in maintaining its course and direction. In flight, the term
"stability" is often equated with the ability of the plane to fly itself.
Stability can either be static or dynamic. Static stability involves only
the return of the disturbed object to its original position. This was the
goal of the early airplane designers; that the airplane would try to
return to its original orientation (position) after a disturbance, such as
a gust of wind. Dynamic stability is concerned with how much time it may
take for the object to return to its original position. If the plane
eventually returns to its original position, then the system is considered
dynamically stable. If it does not, then it is considered dynamically
unstable.
The concept of "control" is a science relating to the human experience in
flying and handling a given aircraft. The concepts are related, because
when "control" is optimized, a given airplane will be relatively easy for
the pilot to fly, and highly stable in flight. The small airplanes used at
local airports are very stable; they are good for both beginning pilots
and the more experienced pilots. They are very easy to fly and very
forgiving of pilot mistakes. Although usually discussed as flight
characteristic, stability and control are equally important during takeoff
and landing.
When the plane is in contact with the runway, sudden movements to the left
or right of the landing surface are disfavored. Stability dictates that
the plane move forwardly and decelerate smoothly during a landing without
sudden "jerkiness." Similarly, as a plane taking off leaves the runway and
breaks contact with the ground, irregular movements caused by
runway-contact can affect flight path stability. One significant cause of
vibration and jerkiness during takeoffs and landings is the tail wheel
assembly, that can vibrate deleteriously when I contact with the runway.
While on the ground, static stability is enhanced by the normal three-point
wheels of the aircraft. Usually a single tail wheel assembly at the
aircraft rear completes the "third point" necessary for establishing a
stable, planar position. With older small planes having "fixed" tail skid
assemblies, the tail skid may be permanently oriented in a position
parallel with the longitudinal axis of the airframe. In some tail wheel
mounting designs, upward or downward movements of the tail wheel are
enabled. However, if the tail wheels are mounted too loosely, they will
shimmy or vibrate during takeoffs and landings. On the other hand, if they
are secured too rigidly, and cannot "give" in response to runway contact,
proper handling can be negatively affected during landings. The time
periods just before liftoff, and during landings, are often critical, and
yet conventional tail wheel mounting assemblies allow the reartovibrate.
The latter problem can be particular vexatious when operating agri-chemical
dispensing airplanes from dirt runways. When the plane takes off, it is
full of fuel and agrichemical, at maximum weight. Jolts or jerking motions
imparted by vibrating tail wheel assemblies during takeoffs can be
disconcerting, to say the least. When the plane returns for a landing, it
is much lighter, and flight characteristics are different than they were
immediately after takeoff. During a landing, when the tail wheel makes
first contact with the landing surface, a "smooth" and non-jerky
transition is desirable. In the fraction of a second that the plane is
neither fully airborne nor fully landed, the path of least resistance for
wheel movement may not be straight down the runway. In other words,
because of wind gusts and numerous other variables, a sleight movement in
tail wheel orientation from "true straightness" can decrease stability.
In other words, during takeoffs and landings especially, conventional tail
wheel assemblies vibrate, rattle, and shimmy. If the tail wheel assembly
is modified to prevent vibration, it must nevertheless be able to "give"
slightly when contacting the ground.
SUMMARY OF THE INVENTION
My new shimmy-preventing tail wheel assembly mounts between a conventional
aircraft tail spring and an original tail wheel fork. A rigid hub assembly
comprises a sleeve-like central hub, that is mated to a lower, cooperating
spindle assembly. A rigid arm projecting from the hub is bolted to the
tail spring. The spindle assembly comprises a rigid, lower flange adapted
to mate with the aircraft tail wheel fork. The spindle assembly is
rotatable relative to the hub assembly, so the tail wheel fork supported
thereby can rotate around its axis.
The spindle assembly comprises a rigid sleeve coaxially extending from a
lower mounting flange through and within the hub assembly. A pair of
bearing assemblies are mounted on opposite ends of the hub assembly. A
special bushing aids in axially pressuring and radially centering the
bearings when they are compressed together. An internal, elongated bolt
extending upwardly from the spindle assembly terminates in a threaded
terminus engaged by a castellated nut that axially secures the bearings
within suitable races fitted on opposite ends of the central hub.
The nut is tightened to approximately one hundred foot pounds of torque to
preload the assembly. This "pre-load" prevents the tail wheel from
swinging freely and shimmying or vibrating. Uncontrolled shimmying results
in dangerous vibration that can cause damage if continued unabated.
However, the dual bearings of the present construction combined with the
weight of the aircraft on the ground, easily rotates the assembly about
the longitudinal axis of the torqued bolt so that the aircraft can
maneuver on the ground with ease. In fact, due to the bearings, the
aircraft is able to move more "freely" than if it only had conventional
metal bushings, as is commonly the situation. The "pre-loading" actually
pits one bearing against the other in a highly unique manner not
originally intended for the bearings.
This synergistic "pre-loading" of the axially spaced-apart bearings
actually acts as a "brake" that makes it impossible for the tail wheel to
shimmy and shake uncontrollably during the critical takeoff and landing
rolls. The special bushing assures that the torque remains constant during
normal operations.
Thus a basic object is to provide a shimmy-free tail wheel mounting
assembly for small aircraft.
Another basic object is to provide an after-market system for mounting tail
wheels that minimizes shimmying and vibration.
Another important object is to provide a tail wheel mounting system of the
character described that is suitable for user-installation.
Conversely, an important object is to provide a system of the character
described that can be installed with new aircraft.
Yet another object is to provide a bushing construction that both radially
centers and axially stresses the bearings.
Another basic object is to provide a highly stable and impact-resistant
tail wheel system for aircraft.
Another important object is to provide an aircraft tail wheel assembly of
the character described that makes it easier to take off and land,
especially on irregular dirt runways or grass landing strips.
A related object is to minimize jarring or jerking effects.
A still further object is to minimize noise, and maximize strength
These and other objects and advantages of the present invention, along with
features of novelty appurtenant thereto, will appear or become apparent in
the course of the following descriptive sections.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following drawings, which form a part of the specification and which
are to be construed in conjunction therewith, and in which like reference
numerals have been employed throughout wherever possible to indicate like
parts in the various views:
FIG. 1 is a fragmentary elevational view of the best mode of my improved
tail wheel mounting system;
FIG. 2 is an enlarged, fragmentary, exploded isometric view, with portions
broken away or shown in section for clarity and/or omitted for brevity;
FIG. 3 is an enlarged frontal isometric view of the preferred mounting
system;
FIG. 4 is a enlarged side view of the preferred mounting system.
FIG. 5 is an enlarged top plan view thereof, taken from a position above
the image of FIG. 4, and looking down;
FIG. 6 is an enlarged, fragmentary, sectional view taken along line 6--6 of
FIG. 5, with portions thereof broken away for clarity or omitted for
brevity;
FIG. 7 is an enlarged, isometric view thereof, taken generally from a
position to the lower left of the image of FIG. 6;
FIG. 8 is an isometric bottom view, taken from a position generally to the
right of the image in Figure;
FIG. 9 is an enlarged view of circled region 9 in FIG. 2; and,
FIG. 10 is an enlarged view of circled region 10 in FIG. 6.
DETAILED DESCRIPTION
With initial reference to FIGS. 1 and 2 of the appended drawings, my
shimmy-free aircraft tail wheel mounting assembly had been generally
designated by the reference numeral 20. System 20 interconnects between a
preexisting aircraft tail spring 22, at the rear of a small airplane, and
the original aircraft tail wheel fork 24. A conventional wheel 26 that
will be recognized by those with skill in the art is mounted by an axle 28
within the arms of the fork 24. Axle 28 penetrates orifice 29 (FIG. 2) in
the fork. A pair of conventional bolts 31, 32 extend through orifices 33
in a fork flange portion 35 (FIG. 2) to mount the fork to the spindle
assembly 40. Specifically, fork flange portion 35 is fastened to spindle
flange 41 with suitable nuts (not shown) that engage bolt 32, that also
penetrate orifices 39 (FIGS. 2, 3) in spindle flange 41. The spindle
assembly 40 comprises the bottom section of the mounting assembly 20, and
is operatively joined to the upper hub assembly 42 for rotation relative
thereto about the industrial grade bolt 49 forming an axle shaft (FIGS. 2,
6). A channel-like arm 44 of the hub assembly 42 securely receives the
tail spring 22 (FIG. 1), being fastened thereto with the combination of
bolts 46 (FIG. 2) that penetrate orifices 48 in arm 44 and compression
nuts 47.
With primary reference now directed to FIGS. 3-4 and 6-8, the spindle
assembly 40 preferably comprises a rigid, elongated sleeve 50 whose hollow
interior communicates with interior bore 52. Sleeve 50 intersects flange
41 (FIG. 7) at an acute angle. Sleeve 50 has a bottom portion 54 integral
with an upper intermediate portion 56 (FIG. 6). Bottom sleeve portion 54
has a larger internal diameter than adjacent, coaxial portion 56. Best
viewed when detached from the hub assembly 42 (FIG. 7), the uppermost
spindle assembly tubular portion 58 (FIG. 7) projects upwardly. Orifice 51
(FIG. 7) facilitates lubrication via external fitting 53 (FIG. 4). Tubular
sleeve portions 54, 56, and 58 are coaxial and integral. An external,
round shoulder flange 60 divides tubular sleeve portions 56, and 58. A
plurality of rigid, elongated and generally rectangular reinforcing webs
62, 62A extend generally longitudinally between the upper shoulder flange
60 and the lower spindle flange 41 (FIG. 7, 8). Web 62A (FIGS. 3, 4) is
welded at its bottom to flange 41. As best appreciated from FIG. 8, webs
62 and 62A are radially spaced apart about the external periphery of
sleeve 50. Each web 62 is welded to shoulder flange 60 at its top, and
terminates in a angled shoulder 65 (FIGS. 6, 7) forming the web bottom.
The rugged, aviation quality, industrial bolt 49 captivated within the
assembly 20 is coaxially disposed within bore 52 (FIG. 6). Bolt 49
comprises a head 70 (FIG. 6) that abuts and is axially restrained by the
shoulder (FIG. 6) formed between sleeve portions 54, 56. The bolt shank 72
extends upwardly though sleeve portion 58, into the hub assembly as
described hereinafter. A threaded terminus 74 (FIGS. 2, 3, 6) integral
with shank 72 receives castellated nut 77 (FIGS. 2, 3, 6) to complete the
assembly. Through experimentation it was found that a special two-segment
bushing 79, best seen in FIGS. 9 and 10 is desirable. Bushing 79 comprises
an annular washer-like top 81 coaxially integral with a lower-diameter
bottom portion 82. During the "preloading" or compression process, when
nut 77 is tightened against bushing 79, the spindle assembly bearings are
compressed together. Bushing 79 compresses the bearings axially, but
bushing segment 82 aligns coaxially within the lower bearing, and tends to
radially center the assembly to insure that relative rotation is possible.
The spindle assembly is thus rotatably coupled to the hub assembly 42.
The rigid hub assembly 42 comprises a rigid, barrel-like hub portion 80
that is integral with the mounting arm 44 projecting angularly away from
it. Arm 44 comprises a pair of spaced-apart and parallel sidewalls 83, 84
(FIG. 3) that are integral with a planar, center portion 85 in which
mounting orifices 48 discussed earlier are defined. The aircraft tail
spring 22 nests snugly between the sidewalls 83, 84 in compressive
engagement with the flat, central arm portion 85. Lubrication of the
interior of hub 80 is facilitated by fitting 85 (FIGS. 4, 6).
As best seen in FIG. 2, the interior of hub 80 comprises an integral ring
portion 86 between a pair of recesses or counterbores 87, 88. Bearings 90,
92 (FIGS. 2, 6) are received within annular races 90A and 92A
respectively. The races 90A, 92A (Fig. are nested coaxially within
counterbores 87, 88, abutting shoulders on opposite sides of ring 86.
Thus, bearings 90, 92 are and the corresponding races are all coaxially
disposed within hub 80. As best seen in FIG. 6, the sleeve portion 58
extending upwardly from the spindle assembly coaxially penetrates the
bearings 90, 92. Relative rotation between the hub assembly and the
spindle assembly is thus enabled.
However, the preloading tension caused by nut 77, which is preferably
torqued to about 100 foot pounds, maintains the assembly relatively
stiffly, preventing it from vibrating or shinmying. However, normal forces
exerted upon the wheel 26 (FIG. 1) when in contact with the runway can
rotatably deflect the spindle assembly to compensate for the various
positional vectors assumed by the alignment of the aircraft, the tail
wheel and the landing surface. While rotation about the longitudinal axis
of bolt 49 is possible during runway contact, preloading of the apparatus
by properly torquing the assembly prevents vibration and shimmying.
From the foregoing, it will be seen that this invention is one well adapted
to obtain all the ends and objects herein set forth, together with other
advantages which are inherent to the structure.
It will be understood that certain features and subcombinations are of
utility and may be employed without reference to other features and
subcombinations. This is contemplated by and is within the scope ofthe
claims.
As many possible embodiments may be made of the invention without departing
from the scope thereof, it is to be understood that all matter herein set
forth or shown in the accompanying drawings is to be interpreted as
illustrative and not in a limiting sense.
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